Polyaryloxyphosphazenes are inherently fire resistant and exhibit very low smoke emission when exposed to fire. They are readily compounded with conventional filters, stabilizers, processing aids, dyes and the like. They are readily cured by peroxides and if they contain some unsaturation, can be cured by sulfur using conventional rubber vulcanizing systems. They are readily foamed and produce excellent fire-resistant, low-smoke, thermal insulating foam which can be used to insulate pipes or walls where such special properties are desired.
Polyaryloxyphosphazenes are conventionally made by reacting a solution of high molecular weight substantially linear polyphosphonitrilic chloride with a solution of an alkali metal phenoxide or substituted phenoxide. Residual alkali metal phenoxide can be neutralized with an acid such as sulfuric acid leaving an impure polyaryloxyphosphazene solution which contains inorganic salts such as sodium chloride and sodium sulfate as well as phenol and/or substituted phenols. Juneau U.S. Pat. No. 4,576,806 discloses a process for removing the inorganic salts by treatment of the neutralized polyaryloxyphosphazene solution with water containing a lower alcohol. This treatment has been found to be very effective in lowering the inorganic salt content of the polyphosphazene.
Polyaryloxyphosphazenes are made using a small stoichiometric excess of alkali metal phenoxide or substituted phenoxides in order to react all or substantially all of the phosphorus-bound chlorine. Upon neutralization in the salt removal stage the phenoxides revert to phenol and substituted phenols. If left in the polymer these impurities impart an objectionable phenolic odor and also result in inferior final products. Therefore, a need exists for a method for removing the phenolic impurities from crude polyaryloxyphosphazene gum.